host api alignment (#7)

* feat: add Firecracker API client methods for VM pause/resume and snapshots

Add PatchVm, GetVm, PutSnapshotCreate, and PutSnapshotLoad methods to the
API client, along with supporting types (VmState, SnapshotCreateParams,
SnapshotLoadParams, MemBackend).

* feat: add snapshot data layer - contract types, model, store, config

Add SnapshotID and snapshot contract types, SnapshotRecord model,
store interface CRUD methods with file store implementation,
snapshot paths helper, SnapshotsDir config, and directory creation.

* feat: add runtime methods for VM pause, resume, snapshot, and restore

Implement Pause, Resume, CreateSnapshot, and RestoreBoot on the
firecracker Runtime. RestoreBoot launches a jailer, stages snapshot
files into the chroot, loads the snapshot, and resumes the VM.

* feat: add daemon snapshot create, restore, and reconciliation logic

Implement CreateSnapshot (pause, snapshot, COW-copy disk, resume),
RestoreSnapshot (COW-copy disk, RestoreBoot, wait for guest),
GetSnapshot, ListSnapshots, DeleteSnapshotByID, and crash recovery
reconciliation for snapshot and restore operations.

* feat: add HTTP endpoints for snapshot create, get, list, delete, restore

Wire 5 snapshot routes: POST /machines/{id}/snapshots (create),
GET /machines/{id}/snapshots (list), GET /snapshots/{id} (get),
DELETE /snapshots/{id} (delete), POST /snapshots/{id}/restore (restore).

* fix: cross-device rename, restore network, and snapshot cleanup

- Replace os.Rename with copy+remove for moving snapshot files out of
  /proc/<pid>/root/ (cross-device link error on Linux)
- Reconfigure network interface after snapshot load so the restored VM
  uses its own tap device instead of the source VM's
- Clean partial snapshot dirs immediately on failure instead of only
  via reconcile
- Reject snapshot requests while a machine operation is already pending

* fix: test and modify snapshot runtime

* feat: snapshot lifecycle update, align runtime issues between host image
and daemon

internal/config/config.go

@@ -18,6 +18,7 @@ type Config struct {
 	OperationsPath        string
 	ArtifactsDir          string
 	MachineDisksDir       string
+	SnapshotsDir          string
 	RuntimeDir            string
 	SocketPath            string
 	EgressInterface       string
@@ -34,6 +35,7 @@ func Load() (Config, error) {
 		OperationsPath:        filepath.Join(rootDir, "state", "ops.json"),
 		ArtifactsDir:          filepath.Join(rootDir, "artifacts"),
 		MachineDisksDir:       filepath.Join(rootDir, "machine-disks"),
+		SnapshotsDir:          filepath.Join(rootDir, "snapshots"),
 		RuntimeDir:            filepath.Join(rootDir, "runtime"),
 		SocketPath:            filepath.Join(rootDir, defaultSocketName),
 		EgressInterface:       strings.TrimSpace(os.Getenv("FIRECRACKER_HOST_EGRESS_INTERFACE")),
@@ -69,6 +71,9 @@ func (c Config) Validate() error {
 	if strings.TrimSpace(c.MachineDisksDir) == "" {
 		return fmt.Errorf("machine disks dir is required")
 	}
+	if strings.TrimSpace(c.SnapshotsDir) == "" {
+		return fmt.Errorf("snapshots dir is required")
+	}
 	if strings.TrimSpace(c.RuntimeDir) == "" {
 		return fmt.Errorf("runtime dir is required")
 	}